The prime mover of the Nature Conservancy and the World Wildlife Fund, who helped inspire nature reserves and ecological research

The conservationist Max Nicholson, who has died aged 98, was director-general of the Nature Conservancy from 1952-66. With Peter Scott and others, he helped create the World Wildlife Fund in 1961; he began, and later was a trustee, of Earthwatch Europe (1985-93). He was also head of the world conservation section of the International Biological Programme. He also had a formidable career of public service; in 1931 he had drafted A National Plan for Britain, which led to the foundation of Political and Economic Planning (PEP). He headed Herbert Morrison's office during the 1945-51 Labour government.
He did not lose his observation with age; in 2000, he drew attention to the decline of sparrows in south-east England, which led to a government grant for research.

He was a catalyst, inspiring people to achievements beyond their own expectations. Perhaps one of his best efforts was the first conference in 1963 of the Countryside In 1970, a programme led by the Duke of Edinburgh; its final and well-supported 1970 conference was a fitting contribution to the European Conservation Year 1970, which had drawn much of its strength from the British environmental movement led by Nature Conservancy.

Max was born in Ireland of English parents, who encouraged his love of natural history, especially birds, from an early age. He was educated at Sedbergh School in Cumbria. At 21 he produced his first book, Birds In England (1926), which was followed by How Birds Live (1927). He then read history at Hertford College, Oxford.

Max not only wrote on birds but conducted censuses, developed counting techniques and worked on bird ecology. And in 1931, as assistant editor of the Weekend Review, he came to write the supplement A National Plan For Britain.

In 1932 he created the British Trust for Ornithology and in 1938 helped found the Edward Grey Institute of Field Ornithology. He co-operated with Ludwig Koch to produce the book with gramophone records, Songs Of Wild Birds (1937), and helped H F Witherby produce the Handbook Of British Birds (1938-41).

Max joined the civil service in 1940, heading the allocation of tonnage division at the Ministry of War Transport, an important post when U-boats were attacking Britain's vital supply convoys. He attended the allied conferences at Cairo, Quebec, Yalta and Potsdam - but he never forgot about birds.

During a deadlocked meeting in Berkeley Square in London, the chairman went with Max to the window to listen to a black redstart. They returned to a dumbfounded gathering and ended the deadlock in two minutes."Never underestimate the power of the bird," said Max.

In 1945 he was given a post in the deputy prime minister's office, which led to him chairing the committee for the 1951 Festival of Britain. More important for the environment and conservation was the opportunity he took in 1949 to draft and steer through the setting up of the Nature Conservancy and the powers it required, including the national parks and access to the countryside Act. This provided for nature reserves and sites of special scientific interest (SSSI).

In 1947-48, with Julian Huxley, the then director general of the United Nations scientific and education organisation Unesco, he was involved in forming the Scientific International Union for Conservation of Nature (IUCN) now the World Conservation Union. From 1945 he had been a member of the committee that had drawn up plans for a command paper for conservation in England and Wales.

During his years as director general of the Nature Conservancy, he needed all his skills to overcome opposition from vested interests, but his ideas and actions came to dominate not only in Britain but many other countries. The Conservancy established, as national reserves and SSSIs, prime sites listed in the command paper. It had expertise in advising on wildlife and on ecological issues affecting the wider environment. The furore over pesticides led to Max setting up Monks Wood experimental station - the first major centre for applied ecological research.

In 1952, Max contracted polio when he was leader of the UN Food And Agricultural Organisation survey team in Baluchistan. This left him with a limp - which made him seem more determined.

He was friends with the giants of the natural sciences who gave freely of their time and made it easy to recruit bright young scientists. His communication skills brought in Peter Scott, James Fisher, David Attenborough and others who helped to change world opinion on environmental responsibilities.

Max was instrumental in setting up the Council For Nature in 1958. He helped found the Conservation Corps (the British Trust for Conservation Volunteers) in 1959 and to develop the Wildlife Trusts Movement. From 1963-74, Max was the influential convenor for conservation of the International Biological Programme. He initiated what is now the Trust for Urban Ecology in 1977 and was president (1980-85) of the Royal Society for the Protection of Birds. He also advised Ladybird Johnson, the wife of US President Lyndon Johnson, on her "beautification of America" programme.

In 1967, Max published The System, an indictment of the inadequacies of the administrative civil service. His The Environmental Revolution was published in 1970. Other books include the nine volumes of The Birds of the Western Palearctic (1977-94). Many of his printed lectures - on conservation and the next renaissance in 1964, and international economic development and the environment in 1970 - eerily prefigure today's "sustainable development". For three years he chaired the groups which produced seven-volumes of The New Environmental Age (1987) applying to Britain the conservation strategy launched in 1980 by IUCN. WWF and Unesco.

Of particular note was his contribution on conservation in The Humanist Frame (1961), edited by Julian Huxley. Shortly after his 90th birthday, he created the New Renaissance Group, which produced Where Next? Reflections On The Human Future (2000) as a guide for the Millennium; this was inspired by The Humanist Frame. He continued to enjoy writing well into his 90s, particularly NRG papers.

He was interested in population issues and was a founder member and chairman of Common Ground International; he was involved with the International Planned Parenthood Federation (IPPF).

Max could be a formidable colleague. His restless imagination and constant striving did not make for an easy life. He would not tolerate any case not founded on thorough research and sound intellectual premises. Yet he could be a considerate companion, and fun.

He is survived by sons Piers and Tom by his first wife, Mary Crawford (died 1995), and by a son David, by his second wife Toni; she died last year.

· (Edward) Max Nicholson, environmentalist, born July 12 1904; died April 26 2003